Encounter Journal Preview
The Encounter Journal is finally on the test realms and even if it isn't finished we finally know how much information we will get from it: a lot. The Firelands raid encounters are already there and it looks like Blizzard really wants you to know where you're going before you enter a raid, see the screenshots below.

I also added a small video preview from OMFGCata because every time I forget to post a video from Jesse, a puppy gets sad.

If you're still wondering how much info you can get for a single fight, check the preview of the Ragnaros encounter below. Everything in the preview (except for the picture, I guess) is from the Encounter Journal and not a single bit of it is from extra datamining.

Ragnaros - Encounter Journal Preview (Heroic Version)
Ragnaros, lord of the Firelands, embodies the fury and destruction of the promordial infernos that forged Azeroth itself. Promised the chance to set Azeroth aflame without interference from Neptulon and Therazane, Ragnaros seeks to appease the Old Gods by incinerating the World Tree of Nordrassil.

When triggered, a Magma Trap erupts for 60000 Fire damage to all enemies within the Firelands and violently knocks the player who stripped the Magma Trap into the air.

An enemy that triggers a Magma Trap will take 50 additional damage from the Magma Trap Eruption for 30 sec. Stacks.

Intermission: Minions of Fire!

At 70% health, Ragnaros will cast Splitting Blow, wedging Sulfuras into the platform and creating Sons of Flame across the platform. Ragnaros will stay submerged for 45 seconds or until all of the Sons of Flame are destroyed.

The Molten Elemental is empowered by nearby Molten Elementals, increasing its damage done by 25% and causing it to be immune to Snare effects.

Intermission: Denizens of Flame!

At 40% health, Ragnaros will cast Splitting Blow, wedging Sulfuras into the platform and creating Sons of Flame. Ragnaros will stay submerged for 45 seconds or until all of the Sons of Flame are destroyed.

The Lava Scion inflicts a random target with Blazing Heat, causing them to create a trail of Blazing Heat in their wake. Blazing Heat inflicts 50000 Fire damage every 1 sec and heals Sons of Flame and Lava Scions for 10% every 1 sec.

The Living Meteor will fixate on a random target and chase them. A player that gets within 4 yards of the Living Meteor will trigger a Meteor Impact, inflicting 500000 Fire damage to enemies within 8 yards.

The Living Meteor is highly Combustible. When attacked, it will cause Combustion, knocking it back several yards away from the enemy that hit it. Combustible is removed for several seconds after Combustion is triggered.

Sulfuras creates a Dreadflame at two nearby Locations. The Dreadflame multiplies rapidly and spreads across the platform. Dreadflame inflicts 35000 Fire damage and an additional 3500 Fire damage every 1 sec for 30 sec.

Cenarius forms a Breadth of Frost at a nearby location. Any Living Meteors that enter the Breadth of Frost are frozen and take 15000% additional damage. Additionally, players who stand within the Breadth of Frost are immune to Superheated damage and have the Superheated debuff removed from them.

Hamuul Runetotem

Hamuul Runetotem is a tauren druid and leads the druids of Thunder Bluff. In Mount Hyjal, he assists Ysera in protecting Nordrassil from Ragnaros. The arch druid will support the raid by entrapping Ragnaros.

Arch Druid Hamuul Runetotem forms Entrapping Roots at a nearby location. If Ragnaros enters the area of the Entrapping Roots, he will become stunned for 10 sec and take 50% additional damage while stunned.

Malfurion Stormrage

Malfurion Stormrage is an ancient and powerful night elf druid. He leads the army of Cenarius in the Defense of Mount Hyjal against the forces of Ragnaros.

Malfurion will support the raid by protecting players from Dreadflame.

Malfurion forms a Cloudburst. The players who interacts with the Cloudburst will be surrounded with a Deluge. Deluge makes the player immune to Dreadflame damage, and also allows the player to extinguish any nearby Dreadflame.

boub, you have overlooked the really BIG thing of this patch: THE KEYCHAIN IS GONE! (No room for it on the bar)
All your keys are now lying about in your bags. You can still bring the window up if you have a keybind to it, but you can't actually put keys in it.

Sounds a lot like the kil'jaeden fight, only a bit more complex. I honestly don't think super hard complex raid fights are what wow needs right now. Not that difficult fights are a bad thing, I'm all for challenging raid content -- I just believe that they should put more effort into actually putting out more content that's interesting. I mean a raid instance is great, but what about the other time I'm not raiding? I'd personally like to see more world events, interaction among players, daily and solo content than "Here's a heroic encounter that's super complex and hard that most people wont even bother to do!" It just feels like they're wasting their time on the wrong kind of content.

i am very surprised they already released heroic version of ragnaros,they always keep end boss under the veil

Until now. With the introduction of the Encounter Journal they're clearly changing their whole take on these things. I think the reasoning goes "the only ones who the secrecy matters for are a dozen of guilds going for world firsts. Everyone else, that is, 99.99% of the WoW subscriber base, will have access to this information from wowhead anyway by the time they even consider reaching it. Catering for the fun of 00.01% or for the 99.99%... let's see..."